selftests: drv-net: test empty queue and NAPI responses in netlink

Make sure kernel doesn't respond to GETs for queues and NAPIs when
link is down. Not with valid data, or with empty message, we want
a ENOENT.

Link: https://patch.msgid.link/20241219032833.1165433-2-kuba@kernel.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>